Enhanced node B, user equipment and methods for discontinuous reception in inter-ENB carrier aggregation

ABSTRACT

Embodiments of user equipment (UE) and methods for enhanced discontinuous reception (DRX) operations for inter eNB carrier aggregation (CA) in an LTE network are generally described herein. In some embodiments, a UE is configured to be served by multiple serving cells. The first set of the serving cells may be associated with a first eNB and a second set of serving cells may be associated with a second eNB. In these embodiments, DRX operations may be performed independently in multiple serving cells belonging to the different eNBs. Other embodiments for enhanced DRX operations are also described.

PRIORITY CLAIM

This application claims priority under 35 U.S.C. 119 to U.S. ProvisionalPatent Application Ser. No. 61/679,627, filed Aug. 3, 2012, which isincorporated herein by reference in its entirety.

TECHNICAL FIELD

Embodiments pertain to wireless communications. Some embodiments relateto discontinuous reception in wireless networks, such as EvolvedUniversal Terrestrial Radio Access (E-UTRA) networks (EUTRANs) operatingin accordance with one of the 3GPP standards for the Long Term Evolution(LTE) (3GPP LTE).

BACKGROUND

One issue with many conventional cellular networks, includingconventional LTE networks, is frequent handover, particularly inheterogeneous deployment scenarios that include macro-cells andpico-cells. For example, a primary cell (PCell) may be served from amacro-cell and a secondary cell (SCell) may be served from a pico-cell.Since the coverage of a pico-cell may be much smaller than that of amacro-cell, user equipment (UE) may need to handover to a macro-cell oranother pico-cell if the UE is connected only to the pico-cell. On theother hand, if the UE is connected to the macro-cell, handover may notbe required, however offloading to the pico-cell would not be provided.To achieve offloading and reduce the frequency of handover, carrieraggregation (CA) between a macro-cell and pico-cell may be performed. Inconventional LTE systems, CA is only supported between cells in the sameenhanced Node B (eNB). However, macro-cells and pico-cells in aheterogeneous deployment scenario may be associated with different eNBs.

In order to reduce power consumption, a UE may engage in discontinuousreception (DRX) operations during which the UE may be configured toreceive a control channel during certain periods of time. The use of CApresents several issues for DRX operations particularly when amacro-cell and a pico-cell are served by different eNBs. For example,when serving cells are associated with different eNBs, it becomesdifficult for a UE to determine the control channel reception times aswell as other DRX related parameters. Other issues associated with theuse of CA for DRX operations when serving cells are associated withdifferent eNBs include uplink scheduling, random access and transmissionof a buffer status report (BSR).

Thus there are general needs for devices and methods that reduce addressthe issues associated with DRX during inter-eNB CA, particularly servingcells are associated with different eNBs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a wireless network in accordance with someembodiments;

FIG. 2 illustrates an example inter-eNB CA deployment scenario inaccordance with some embodiments;

FIG. 3 illustrates the exchange of bitmaps for DRX active timedetermination in accordance with some embodiments;

FIG. 4 illustrates time-domain multiplexing for uplink scheduling inaccordance with some embodiments; and

FIG. 5 illustrates a wireless communication device in accordance withsome embodiments.

DETAILED DESCRIPTION

The following description and the drawings sufficiently illustratespecific embodiments to enable those skilled in the art to practicethem. Other embodiments may incorporate structural, logical, electrical,process, and other changes. Portions and features of some embodimentsmay be included in, or substituted for, those of other embodiments.Embodiments set forth in the claims encompass all available equivalentsof those claims.

FIG. 1 illustrates a wireless network in accordance with someembodiments. Wireless network 100 includes user equipment (UE) 102 and aplurality of enhanced node Bs (eNBs) 104, 106 and 116. The eNBs mayprovide communication services to UEs, such as UE 102. The eNB 104 maybe a serving eNB when the UE 102 is located with a region served by eNB104. The eNBs 106, 116 may be neighbor eNBs. Each eNB may be associatedwith a set of one or more serving cells that may include macro-cells andpico-cells.

In some of these embodiments, eNB 104 and eNB 106 may engage ininter-eNB carrier aggregation (CA), although the scope of theembodiments is not limited in this respect. For inter-eNB CA two or morecomponent carriers of different cells may be aggregated to serve asingle UE (i.e., UE 102). For example, the UE 102 may receive resourceblocks of the same downlink channel 107 from two or more eNBs (e.g., eNB104, eNB 106, and eNB 116).

In some embodiments, the downlink channel 107 that the UE 102 mayreceive from two or more eNBs may be a physical downlink shared channel(PDSCH). In some embodiments, the downlink channel 107 that the UE 102may receive from two or more eNBs may be a physical downlink controlchannel (PDCCH). In some embodiments, UE 102 may be configured forcoordinated multi-point (CoMP) operations in which one or more downlinkchannels 107 are at least partially offloaded from a serving eNB 104 toone or more neighbor eNBs 106, 116.

FIG. 2 illustrates an example inter-eNB CA deployment scenario inaccordance with some embodiments. In these embodiments during whichinter-eNB CA is performed, rather than a handover process, a secondarycell addition-removal process may be performed as the UE 102 transitionsamong secondary cells 206, 216 within a primary cell 204. In theseembodiments, data may be offloaded from the primary cell 204 to one ormore of secondary cells 206, 216 helping to reduce the bandwidthrequirements of the primary cell 204. In the example illustrated in FIG.2, the primary cell 204 may be a macro-cell and the secondary cells 206,216 may be pico-cells, however this is not a requirement. As shown inFIG. 2, UE 102 may be served by macro-cell 204 at time t1, may addpico-cell 206 at time t2, may remove pico-cell at time t3, may addpico-cell 216 at time t4, and may remove pico-cell 216 at time t5.

In accordance with some embodiments, DRX operations may be performedindependently in multiple serving cells belonging to the different eNBs.In these embodiments, the UE 102 may be configured for DRX operationsand may be served by multiple serving cells including a primary cell(PCell) and one or more secondary cells (SCell). A first set of theserving cells being associated with a first eNB 104 and a second set ofserving cells being associated with a second eNB 106. In theseembodiments, the UE 102 may be configured with DRX parameters for afirst DRX operation for the serving cells of the first set. The DRXparameters for the first DRX operation may be the same for all servingcells of the first set. The 102 may be configured with DRX parametersfor a second DRX operation for the serving cells of the second set. TheDRX parameters for the second DRX operation may have at least asame/common active time for DRX operation. The UE 102 may determine afirst active time, based on the first DRX parameters, in which the UE102 is to monitor a control channel (e.g., the PDCCH) of the servingcells of the first set based on the first DRX parameters. The UE 102 maydetermine a second active time, based on the second DRX parameters, inwhich the UE 102 is to monitor a control channel (e.g., the PDCCH) ofthe serving cells of the second set.

In these embodiments, DRX operations may be managed fully independent inmultiple serving cells. The active time may be managed independentlywith the different DRX related parameters. The UE 102 may monitor thePDCCH in the different subframes depending on the serving cells in thedifferent eNB. The UE 102 can receive the different DRX relatedparameters for the serving cells. In these embodiments, the same DRXrelated parameters and active time are applied for serving cellsassociated to the same eNB.

In some of these embodiments, the first eNB 104 and the second eNB 106may communicate over an X2 interface 110. Since a different DRXconfiguration may be applied for the serving cells in the differenteNBs, any delay over the X2 110 interface does not affect DRXoperations. In these embodiments, all DRX parameters may be the same forserving cells belonging to the same eNB. Different DRX parameters may beused for serving cells belonging to different eNBs.

In some embodiments, the serving cells of the first set (e.g., theserving cells associated with the first eNB 104) may comprise an eNBspecific cell group (ECG) (i.e., a first ECG). The serving cells of thesecond set (e.g., the serving cells associated with the second eNB 106)may also comprise an ECG (i.e., a second ECG). An ECG may refer to a setof serving cells associated to a single eNB.

In some embodiments, when some of the serving cells are provideddifferent eNBs, the UE 102 may monitor the PDCCH in different subframesfor serving cells associated with the first and second eNBs to receivethe first and second DRX parameters. Since some of the serving cells areprovided by different eNBs, the UE 102 monitors the PDCCH in differentsubframes for the serving cells of the different eNBs to receive the DRXparameters.

In some embodiments, the active time for serving cells of each setincludes time while one or more timers associated with the serving cellsof the set are running. The timers may include an on-duration time, aDRX-inactivity timer, a DRX-retransmission timer, and a MACcontention-resolution timer. In these embodiments, the active time ofserving cells of each set may be defined with different timers.

In some embodiments, the active time for serving cells for each set mayfurther include time while a scheduling request sent by the UE 102 on aphysical uplink control channel (PUCCH) in one of the serving cells ofthat set is pending. Accordingly, each set of serving cells may have adifferent active time. In these embodiments, the UE 102 may beconfigured to send a scheduling request on the PUCCH in one of theserving cells.

In some embodiments, the active time further includes time while anuplink grant for a pending hybrid-automatic repeat request (HARQ)retransmission can occur and there is data in a corresponding HARQbuffer of one of the serving cells of that set. In some embodiments, fora primary cell associated with the first eNB 104, the active time mayalso include time while PDCCH indicating a new transmission addressed tothe UE 102 has not been received after reception of a random accessresponse for a preamble not selected by the UE 102.

As discussed above, when the eNBs are engaged in inter-eNB CA, the UE102 may receive a downlink channel from two or more eNBs. In theseembodiments, the UE 102 may process aggregated component carriers of thedifferent serving cells of a set in single FFT operations, although thisis not a requirement. In these embodiments, the component carriers maybe continuous or discontinuous in frequency.

In some embodiments, the UE 102 may receive a radio-resource control(RRC) message at connection establishment from a serving eNB 104. Themessage may indicate the DRX parameters for each set of serving cells.The UE 102 may perform to a DRX operation for each set of serving cellsbased on different sets of DRX parameters. In some embodiments, a singleRRC message by the serving eNB may be used to indicate the DRXparameters for both sets of serving cells. In other embodiments,separate RRC messages may be used.

In these embodiments, the serving eNB 104 may send an RRC message to theUE 102 at connection establishment to indicate the DRX parameters per aset of serving cells belonging to the same eNB. The UE 102 may performDRX operations in each serving cell belonging to the same eNB.

In some embodiments, each eNB may transmit a message to indicate the DRXparameters for the serving cells associated with said eNB. In someembodiments, the message may be a DRX-config-sECG message.

The following shows the example of RRC signaling to configure differentDRX parameters for multiple eNBs. The current DRX parameters can be usedfor the eNB including the PCell. For the eNB not including the PCell, aDRX-Config-sECG may be used. Although the active time is appliedindependently and DRX related timers are managed independently per ECG,the same or different value for the DRX related timers can beconfigured. In this case, the following new parameters may not beneeded.

DRX-Config ::= CHOICE { release NULL, setup SEQUENCE { onDurationTimerENUMERATED { psf1, psf2, psf3, psf4, psf5, psf6, psf8, psf10, psf20,psf30, psf40, psf50, psf60, psf80, psf100, psf200}, .... }DRX-Config-sECG ::= CHOICE { release NULL, setup SEQUENCE {onDurationTimer ENUMERATED { psf1, psf2, psf3, psf4, psf5, psf6, psf8,psf10, psf20, psf30, psf40, psf50, psf60, psf80, psf100, psf200}, ....

In some embodiments, the active time for DRX operation is the timeduring which the UE monitors the PDCCH in PDCCH-subframes. The OnDuration Timer specifies the number of consecutive PDCCH-subframe(s) atthe beginning of a DRX Cycle. The DRX-Inactivity Timer specifies thenumber of consecutive PDCCH-subframe(s) after successfully decoding aPDCCH indicating an initial uplink (UL) or downlink (DL) user datatransmission for this UE. The DRX Retransmission Timer specifies themaximum number of consecutive PDCCH-subframe(s) for as soon as a DLretransmission is expected by the UE. The MAC-contention resolutiontimer specifies the number of consecutive subframe(s) during which theUE shall monitor the PDCCH after an Msg3 is transmitted. In some LTEembodiments, Msg3 may carry the RRC connection request message from UEas part of a random access procedure utilizing a random access channel(RACH).

In some embodiments, a DRX cycle includes at least an on-duration timeand a DRX cycle length. The on-duration time may be the period of time(i.e., the active time) of the DRX cycle length during which the UE 102is configured to monitor the PDCCH. The DRX cycle length indicates aperiodic repetition for a DRX cycle that includes the on-duration timefollowed by an opportunity for DRX time during which the UE is in alow-power state and does not transmit or receive data. The DRXparameters may include the on-duration time and a DRX cycle length. TheDRX parameters may also include an inactivity time.

In some embodiments, DRX operations may be managed partiallyindependently in multiple serving cells. In these embodiments, whenactive time operations are unrelated to instantaneous PDCCH reception orHARQ status, the active time operation remains the same (i.e.,synchronized between the serving cells). For example the active time ofserving cells may be configured to be common between of the first andsecond sets (i.e., the active times are synchronized and appliedcommonly to all serving cells). When the active time operations arerelated to instantaneous PDCCH reception or HARQ status, the activetimes for the serving cells of the first set and for the serving cellsof the second set may be independently determined by the first andsecond eNBs 104, 106 (i.e., the active time operations are managedindependently per eNB, not applied commonly and not necessarysynchronized).

Table 1 shows examples of active time management in inter-eNB CA inaccordance with some embodiments. The event column refers to when theactive time is enabled. Each event may be started when the conditiondescribed in the second column is met. The third column describeswhether the active time due to the corresponding event is commonlyapplied to all serving cells or independently applied for serving cellsof a different eNB. Even in case of independent active time management,the active time may be applied commonly for all serving cells associatedto the same eNB to maintain the Rel-10 CA operation. Except for the onDuration Timer, all events are related to grant, HARQ status or PCell.The mac-Contention Resolution Timer may be started when Msg3 istransmitted on the PCell for collision resolution. In this case, theactive time may be enabled on the PCell only or for serving cellsassociated with the same eNB with PCell.

If the active time is independently managed, the different DRX relatedtimer value can be configured per eNB. Alternatively, even if the activetime is independently managed, the same DRX related timer value can beconfigured for all serving cells.

TABLE 1 Active Time Management Common or Event Condition for start ofEvent Independent on Duration Timer is running Subframe corresponding toDRX Common start offset and short or long DRX cycle DRX-Inactivity Timeris running When the UE receives initial UL Independent or DL grantDRX-Retransmission Timer is When a HARQ RTT Timer expires independentrunning in this subframe and the data of the corresponding HARQ processwas not successfully decoded MAC-Contention Resolution Timer When Msg3is transmitted on the Only for serving cells is running PCell associatedwith same eNB with PCell. a Scheduling Request(SR) is sent on When SR issent on PUCCH independent PUCCH and is pending an uplink grant for apending HARQ When there is a pending HARQ Independent retransmission canoccur retransmission. a PDCCH indicating a new When Msg2 is receivedIndependent transmission addressed to the C- RNTI of the UE has not beenreceived after successful reception of a RAR for the preamble notselected by the UE

FIG. 3 illustrates the exchange of bitmaps for DRX active timedetermination in accordance with some embodiments. In these embodiments,primary and secondary eNBs are configured to exchange information in theform of bitmaps that indicate their expected active times. The expectedactive time for the next interval is indicated by the union of both ofthese bitmaps.

In some of these embodiments, an eNB 104 operating as a primary eNB(PeNB) including a primary cell (PCell) may be configured to send aPCell bitmap 304 via an X2 interface 110 to a secondary eNB (SeNB)including a secondary cell (SCell). The PCell bitmap 304 may indicate anexpected active time for the UE 102 for a first set of serving cellsincluding the primary cell. The primary eNB 104 may also receive a SCellbitmap 306 via the X2 interface 110 from the secondary eNB. The SCellbitmap 306 may indicate an expected active time for the UE 102 for asecond set of cells including the secondary cell.

The primary eNB 104 may determine a final active time 314 for a nexttime interval 312 based the combination (i.e., union) of both the PCellbitmap 304 and the SCell bitmap 306. The primary eNB 104 may alsotransmit a physical downlink control channel (PDCCH) during the finalactive time. Each bit of the PCell bitmap 304 and the SCell bitmap 306may indicate whether a time interval 310 of a predetermined time period308 is active. The predetermined time period 308 may be at least asgreat as an X2 interface delay time. In these embodiments, the finalactive time 314 includes times that either bitmap indicates as active,as illustrated in FIG. 2. Accordingly, the active times can besynchronized in inter-eNB carrier aggregation.

In some embodiments, multiple serving cells may be configured to belongto the primary eNB. In these embodiments, one of multiple serving cellsmay be the primary cell.

In some embodiments, an eNB, such as serving eNB 104, may indicate topeer eNBs (e.g., eNBs 106, 116) events which change the active time. Inthese embodiments, the serving eNB 104 may be engaged in inter-eNBcarrier aggregation with a neighbor eNB 106. The serving eNB 104 may beconfigured to send an indication to a neighbor eNB 106 of an event thatchanges an active time of a DRX cycle for a UE. The indication may besent over the X2 110 interface at least a predetermined period (e.g., Xms) before the active time is to be changed. The predetermined timeperiod may be at least as great as an X2 interface delay time betweenthe serving eNB and the neighbor eNB. In response to the indication, theneighbor eNB 106 may be to reconfigure the DRX cycle for the UE inaccordance with the indication so that both the serving eNB and theneighbor eNB operate in accordance with the same DRX cycle for the UE.

In some embodiments, the indication may include an event type and acorresponding time stamp. The time stamp may indicate a system framenumber and a subframe number at which the changes in the active time ofthe DRX cycle are to start. In some embodiments, the events may includeone or more of an initiation of a new downlink or uplink transmissionwhen an on-Duration Timer is not running, a retransmission which stops aDRX-Retransmission Timer, and/or a transmission of a DRX Command MACcontrol element. In these embodiments, the eNB may send events whichchange the active time to a peer eNB via X2 signaling.

In some embodiments, the time interval 310 may be a multiple of one ormore subframes. The subframes may comprise subframes configured inaccordance with a 3GPP LTE standard. In these embodiments, each subframemay be one millisecond (ms) long, although this is not a requirement.

In some embodiments, the primary eNB 104 may be arranged to send thePCell bitmap 304 to the secondary eNB 106 at least the predeterminedtime period 308 (e.g., X ms) before a start of the next time interval312. The predetermined time period may be at least as great as an X2interface delay time between the primary and secondary eNBs. Thesecondary eNB 106 may send the SCell bitmap 306 to the primary eNB 104at least the predetermined time period 308 before the next time interval312. Accordingly, the secondary eNB 106 will have the bitmap for thenext time interval 312 prior to the start of the next time interval 312,and the primary eNB 104 will have the SCell bitmap for the next timeinterval 312 prior to the start of the next time interval 312. The X2interface delay time may range from as little as 10 ms to as great as 20ms or more.

In some embodiments, the primary eNB 104 and the secondary eNB 106 mayexchange their bitmaps 304, 306 once every predetermined time period308.

In these embodiments, the primary eNB 104 may determine the PCell bitmap304 and may can estimate the possible active time based on ownscheduling decision or DRX related parameters. The UE 102 determines theactive time based on DRX related parameters and active time triggeringevents. The UE 102 may monitor the PDCCH every subframe if the subframeis considered as active time. The UE 102 may receive downlink data in asubframe which is designated as active time. The UE 102 may transmituplink data when scheduled regardless of whether the uplink subframe isactive or not. The active time may include one or more subframes 310.

In these embodiments, the UE 102 treats PDCCHs from the different eNBsas if it is from the same eNB. To be synchronized on the active timebetween eNBs, the eNBs exchange its scheduling behavior over the X2interface 110. In the example illustrated in FIG. 3, the eNBs exchangethe expected UE active time every time interval 308, which includes 20sub-frames 310 totaling 20 ms. In this example, the expected active timeis 20 bits. PeNB 304 refers to the eNB including the PCell and SeNBrefers the eNB not including the PCell. As illustrated in FIG. 3, theunion of the expected active time is the final active time for the nexttime interval 318 (e.g., for the next 20 ms).

Another issue with inter-eNB CA is uplink scheduling. Conventionally,different eNBs may schedule uplink (UL) transmissions independently. Asa result, the aggregated UL transmission power of all serving cells mayexceed a maximum allowed UL transmission power. The UE may need to scaledown transmission power to comply with the power limitation andcorresponding PUSCH or PUCCH performance may be degraded.

In accordance with some embodiments, eNBs may be configured to exchangethe required transmission power for its own PUSCH scheduling and/orPUCCH transmission via the X2 interface 110 in a semi-static way. Forexample, a macro-eNB may indicate to a pico-eNB a maximum transmissionpower allowed in its set of pico-cells (e.g., P_(ECG)). Based on theconfiguration, the pico-eNB may set corresponding P_(CMAX,c) for eachserving cell. Alternatively, the eNBs may be configured with the allowedpower headroom for their own PUSCH scheduling and/or PUCCH transmissionvia the X2 interface. The allowed power headroom may indicate anallowable amount of power increase with respect to the current transmitor receive power or with respect to a reference transmit or receivedpower.

In some of these embodiments, a serving eNB, such as eNB 104 may beengaged in inter-eNB carrier aggregation (CA) with a neighbor eNB 106.In these embodiments, eNB 104 may exchange transmission powerinformation for own PUSCH scheduling and/or PUCCH transmission over anX2 interface 110 with eNB 106. The transmission power information mayinclude, for example, an indication of a maximum transmission power tobe used by the neighbor eNB 106 within a set of serving cells associatedwith the neighbor eNB 106. The serving eNB 104 may be a macro-eNB andthe neighbor eNB is a pico-eNB, although this is not a requirement.

FIG. 4 illustrates time-domain multiplexing for uplink scheduling inaccordance with some embodiments. In these embodiments, a time domainmultiplexing (TDM) solution is provided. In these embodiments, for oneUL subframe, the UE 102 may only transmit the PUSCH/PUCCH to one ECG(i.e. the serving cell(s) associated with one eNB). The eNBs mayexchange information for a TDM partition the X2 interface 110. Asillustrated in FIG. 4, a macro-eNB (an eNB associated with a macro-cell)may provide to a pico-eNB (an eNB associated with a pico-cell) a bitmap402 that indicates the subframes 404 where the UE 102 will transmit tothe serving cell(s) associated with the macro-eNB. Alternatively, themacro-eNB may provide the pico-eNB with DL bitmap that indicates wherethe macro-eNB will operate in the downlink. In some LTE embodiments, thetiming between the PUSCH/PUCCH and a corresponding DL transmissionfollows a predefined rule and therefore such a DL bitmap may determineUL activity.

In some alternate embodiments, an eNB may exchange different bitmap(i.e., one bitmap for downlink scheduling and another bitmap other foruplink scheduling). Alternatively, for uplink scheduling, two differentbitmaps may be exchanged (e.g., one for PUSCH transmissions and otherfor PUCCH transmissions).

In some of these embodiments, the length of a bitmap may take intoaccount some factors including the HARQ timing relationship and/orperiod. In an example embodiment discussed below for frequency domainduplexing (FDD), an eight millisecond (ms) bitmap (i.e., “10000000”) isused. When a pico-NB receives such a bitmap, it determines that the UE102 may only transmit the PUSCH and/or the PUCCH to macro-cells inaccordance with the bitmap (e.g. in (SFN #0, subframe 0 and 8), (SFN #1,subframe #6), etc. as shown in FIG. 4).

In these embodiments, a serving eNB 104 may be engaged in inter-eNB CAwith a neighbor eNB 106. The serving eNB 104 may generate a bitmap toindicate subframes during which the UE 102 is to transmit to the servingeNB 104. The serving eNB 104 may provide the bitmap to the neighbor eNB106 over an X2 interface.

In some other embodiments, an eNB 104 may use dynamic X2 signaling overthe X2 interface 110 to exchange information related to UL scheduling.For example, whenever a macro-eNB is to transmit DL data or schedule theUE 102 to transmit UL data, the macro-eNB may notify pico-eNB via X2signaling. In some embodiments, the notification information may includethe subframe information (e.g., the SFN and subframe index of theevent), the type of the event (e.g. a DL transmission or an ULtransmission) and/or the UL transmission power.

In these embodiments, the serving eNB 104 may engage in dynamic X2signaling over the X2 interface 110 to exchange information related touplink scheduling. As part of the dynamic X2 signaling, the serving eNB104 may notify the neighbor eNB 106 that the serving eNB 104 is toeither transmit downlink data to schedule a UE to transmit uplink data.The notification may include one or more of subframe information, typeof event and uplink transmission power. The subframe information may asubframe index. The type of event may include either a downlinktransmission or an uplink transmission.

Another issue with inter-eNB CA is random access. When a pico-cell isadded as one of the serving cells, UE 102 conventionally may perform arandom access procedure to access the pico-cell. However there may be nocommunication between macro-cell and pico-cell, therefore macro-cell isnot aware whether the random access to the pico-cell is successful ornot.

When UE sends a random access preamble in SCell, a Random AccessResponse (RAR) may be sent from the PCell. In accordance with someembodiments for inter-eNB CA, the RAR may be transmitted from pico-cell(SCell) directly. In these embodiments, the pico-cell may be configuredto transmit the RAR to the UE 102 and the UE 102 may be configured tomonitor the PDCCH of the SCell for RAR reception.

In some embodiments, once the Random Access Preamble is transmitted andregardless of the possible occurrence of a measurement gap, the UE 102may monitor the PDCCH of the PCell or SCell of the secondary ECG. TheRandom Access Preamble is transmitted in the corresponding SCell forRandom Access Response(s) identified by the RA-RNTI, in the RA Responsewindow which starts at the subframe that contains the end of thepreamble transmission plus three subframes and has lengthra-ResponseWindowSize subframes. Some of these embodiments may beperformed in accordance with 3GPP TS 36.321, release 11 or later.

In some other embodiments, a pico-cell may be configured to performRandom Access Preamble detection and may reports the detected RandomAccess Preamble to the macro-cell (PCell) via X2 signaling. Then RAR maybe transmitted from PCell. The X2 signaling may include the subframe andan index of the corresponding PRACH detected.

In accordance with embodiments, the macro-cell may be informed aboutrandom access has been successful or unsuccessful. In some of theseembodiments, a pico-cell may inform macro-cell via X2 signaling. Asdescribed above, if the pico-cell indicates to the macro-cell about thedetected Random Access preamble, the macro-cell determines that therandom access is successful. In these embodiments, the pico-cell mayalso indicate to the macro-cell that the random access has failed whenpico-cell cannot detect Random Access Preamble within a specified time(e.g. based on a timer).

In some other embodiments, the macro-cell may start a timer (e.g.picoRATimer) after it indicates to the UE 102 and the pico-cell that theUE 102 is to perform random access at the pico-cell. If the macro-eNBdoes not receive any indication either from pico-cell or from the UE102, the macro-eNB may consider that random access to pico-cell failed.

In some other embodiments, after the UE 102 receives a RAR from thepico-cell, the UE 102 may report this information to the macro-cell. TheUE 102 may report this information using physical layer signal (e.g.another Random Access Preamble), a MAC Control Element, or a new UL RRCmessage.

Another issue with inter-eNB CA is the buffer status report (BSR). Inaccordance with embodiments, the UE 102 may send a Scheduling Request(SR) to the eNB to inform the eNB that the UE 102 has an unspecifiedamount of data to send. The UE may send a BSR to report pending data inuplink buffers. In some embodiments, the BSR may inform the eNB that theamount of data that the UE 102 has to send is within a predefined range.The amount of data available may be specified for logical channel groupsrather than individual bearers, although this is not a requirement.Conventionally, a short BSR is used only for the highest prioritychannel, which may not be optimized for inter-eNB CA operations. Inaccordance with these embodiments, the UE 102 may transmit a short BSRto each ECG independently. In other words, the UE 102 may transmit ashort BSR to each eNB independently. Since the BSR is controlled bytimers (e.g., a retxBSRTimer, and a periodicBSR-Timer), each ECG mayhave a separate timer. In these embodiments, when the UE 102 isconfigured with multiple ECGs due to inter-eNB CA, the UE 102 maymaintain independent retxBSR-Timer and periodicBSR-Timer for each ECG.

In accordance with some embodiments, the UE 102 may perform a bufferstatus reporting procedure in which the UE 102 may consider all radiobearers which are not suspended and may consider radio bearers which aresuspended. If the UE 102 is configured with multiple ECGs, the UE 102may maintain independent retxBSR-Timer and periodicBSR-Timer for eachECG. In these embodiments, a Buffer Status Report (BSR) may be triggeredif any of the following events occur:

-   -   UL data, for a logical channel which belongs to a LCG, becomes        available for transmission in the RLC entity or in the PDCP        entity and either the data belongs to a logical channel with        higher priority than the priorities of the logical channels        which belong to any LCG and for which data is already available        for transmission, or there is no data available for transmission        for any of the logical channels which belong to a LCG, in which        case the BSR is referred below to as “Regular BSR”;    -   UL resources are allocated and number of padding bits is equal        to or larger than the size of the Buffer Status Report MAC        control element plus its subheader, in which case the BSR is        referred below to as “Padding BSR”;    -   retxBSR-Timer expires and the UE has data available for        transmission for any of the logical channels which belong to a        LCG, in which case the BSR is referred below to as “Regular        BSR”;    -   periodicBSR-Timer expires, in which case the BSR is referred        below to as “Periodic BSR”.

For Regular and Periodic BSR:

-   -   if more than one LCG belongs to the same ECG has data available        for transmission in the TTI where the BSR is transmitted: report        Long BSR;    -   else report Short BSR.

For Padding BSR:

-   -   if the number of padding bits is equal to or larger than the        size of the Short BSR plus its subheader but smaller than the        size of the Long BSR plus its subheader:        -   if more than one LCG belongs to the same ECG has data            available for transmission in the TTI where the BSR is            transmitted: report Truncated BSR of the LCG with the            highest priority logical channel with data available for            transmission;        -   else report Short BSR.    -   else if the number of padding bits is equal to or larger than        the size of the Long BSR plus its subheader, report Long BSR.        In these embodiments, when the UE 102 is configured with        multiple ECGs, the UE 102 may transmit a short BSR to        corresponding ECG. Some of these embodiments may be performed in        accordance with 3GPP TS 36.321, release 11 or later.

FIG. 5 is a functional block diagram of a UE in accordance with someembodiments. UE 500 may be suitable for use as UE 102 (FIG. 1) althoughother UE configurations may also be suitable. UE 500 may include atransceiver 504 for communicating with at least two or more eNBs andprocessing circuitry 502 configured to perform at least some of theoperations described herein. UE 500 may also include a memory and otherelements not separately illustrated. The processing circuitry 502 mayalso be configured to determine several different feedback valuesdiscussed below for transmission to an eNB. The processing circuitry mayalso include a media access control (MAC) layer. In some embodiments,the UE 500 may include one or more of a keyboard, a display, anon-volatile memory port, multiple antennas, a graphics processor, anapplication processor, speakers, and other mobile device elements. Thedisplay may be an LCD screen including a touch screen.

The one or more antennas utilized by the UE 500 may comprise one or moredirectional or omnidirectional antennas, including, for example, dipoleantennas, monopole antennas, patch antennas, loop antennas, microstripantennas or other types of antennas suitable for transmission of RFsignals. In some multiple-input multiple-output (MIMO) embodiments, theantennas may be effectively separated to take advantage of spatialdiversity and the different channel characteristics that may resultbetween each of antennas and the antennas of a transmitting station.

Although the UE 500 is illustrated as having several separate functionalelements, one or more of the functional elements may be combined and maybe implemented by combinations of software-configured elements, such asprocessing elements including digital signal processors (DSPs), and/orother hardware elements. For example, some elements may comprise one ormore microprocessors, DSPs, application specific integrated circuits(ASICs), radio-frequency integrated circuits (RFICs) and combinations ofvarious hardware and logic circuitry for performing at least thefunctions described herein. In some embodiments, the functional elementsmay refer to one or more processes operating on one or more processingelements.

In some embodiments, the UE 500 may be configured to transmit andreceive OFDM communication signals over a multicarrier communicationchannel in accordance with an OFDMA communication technique. The OFDMsignals may comprise a plurality of orthogonal subcarriers. In some LTEembodiments, the basic unit of the wireless resource is the PhysicalResource Block (PRB). The PRB may comprise 12 sub-carriers in thefrequency domain×0.5 ms in the time domain. The PRBs may be allocated inpairs (in the time domain). In these embodiments, the PRB may comprise aplurality of resource elements (REs). A RE may comprise onesub-carrier×one symbol.

In some embodiments, the UE 500 may be part of a portable wirelesscommunication device, such as a personal digital assistant (PDA), alaptop or portable computer with wireless communication capability, aweb tablet, a wireless telephone, a wireless headset, a pager, aninstant messaging device, a digital camera, an access point, atelevision, a medical device (e.g., a heart rate monitor, a bloodpressure monitor, etc.), or other device that may receive and/ortransmit information wirelessly.

In some UTRAN LTE embodiments, the UE 500 may calculate severaldifferent feedback values which may be used to perform channel adaptionfor closed-loop spatial multiplexing transmission mode. These feedbackvalues may include a channel-quality indicator (CQI), a rank indicator(RI) and a precoding matrix indicator (PMI). By the CQI, the transmitterselects one of several modulation alphabets and code rate combinations.The RI informs the transmitter about the number of useful transmissionlayers for the current channel, and the PMI indicates the codebook indexof the precoding matrix (depending on the number of transmit antennas)that is applied at the transmitter. The code rate used by the eNB may bebased on the CQI. The PMI may be a vector or matrix that is calculatedby the UE and reported to the eNB. In some embodiments, the UE maytransmit the PUCCH of format 2, 2a or 2b containing the CQI/PMI or RI.

Embodiments may be implemented in one or a combination of hardware,firmware and software. Embodiments may also be implemented asinstructions stored on a computer-readable storage device, which may beread and executed by at least one processor to perform the operationsdescribed herein. A computer-readable storage device may include anynon-transitory mechanism for storing information in a form readable by amachine (e.g., a computer). For example, a computer-readable storagedevice may include read-only memory (ROM), random-access memory (RAM),magnetic disk storage media, optical storage media, flash-memorydevices, and other storage devices and media. In some embodiments, oneor more processors may be configured with instructions stored on acomputer-readable storage device.

The Abstract is provided to comply with 37 C.F.R. Section 1.72(b)requiring an abstract that will allow the reader to ascertain the natureand gist of the technical disclosure. It is submitted with theunderstanding that it will not be used to limit or interpret the scopeor meaning of the claims. The following claims are hereby incorporatedinto the detailed description, with each claim standing on its own as aseparate embodiment.

What is claimed is:
 1. An enhanced Node B (eNB) to operate as a servingeNB and engage in inter-eNB carrier aggregation with a neighbor eNB, theeNB comprising interface circuitry arranged to: send an indication tothe neighbor eNB of an event that changes an active time fordiscontinuous reception (DRX) operations for user equipment (UE), theindication to be sent over an X2 interface at least a predeterminedperiod before the active time is to be changed, the predetermined timeperiod being at least as great as an X2 interface delay time between theserving eNB and the neighbor eNB, the X2 interface being used forcommunication between the serving eNB and the neighbor eNB; and instructthe UE to perform DRX operations in serving cells associated with theserving eNB in accordance with the changed active time, wherein inresponse to the indication, the neighbor eNB is to reconfigure DRXoperations for the UE to perform DRX operations in serving cellsassociated with the neighbor eNB in accordance with the changed activetime, the changed active time being a same active time for serving cellsof both eNBs.
 2. The serving eNB of claim 1 wherein the indicationincludes an event type and a corresponding time stamp, the time stampindicating a system frame number and a subframe number at which theactive time is to be changed.
 3. The serving eNB of claim 2 wherein theevent types include: an initiation of a new downlink or uplinktransmission when an on-duration timer is not running; a retransmissionwhich stops a DRX-retransmission timer; and a transmission of a DRXcommand media-access control (MAC) control element.
 4. The serving eNBof claim 1 further configured to: configure a secondary cell to performrandom access preamble detection and to report a detection of a randomaccess preamble using X2 signaling; and either transmit a random-accessresponse (RAR) to the UE within a primary cell or configure thesecondary cell to transmit the RAR.